Lay-in connectors characteristically have a body or first member that is generally channel-shaped when viewed endwise, and a top screw-threaded second member, plus a screw through the top member to be tightened against a conductor or conductors laid in the connector. The first member has a base portion and upstanding walls. In-turned marginal portions or overhangs on the walls cooperate with the screw-threaded member, to resist upward thrust of the latter when its screw is tightened. The cooperating surfaces of the overhangs and of the top member slope inward and downward, so that any upward thrust of the screw-bearing member against the overhangs serves to develop inward force on the overhangs, guarding against spreading of the walls of the body or first member.
The screw-threaded member is completely removed from the base member when a conductor is to be laid into place between the walls of the first member. Then the screw-threaded member is shifted into position over the conductor but below the overhangs. Tightening of the screw squeezes the inserted conductor against the base portion and deforms the conductor (or conductors) outward against the walls of the base member.
While the overhangs resist spreading of the walls along their top margins, there is a tendency of the walls, when tall and thin, to bulge outward due to one or more conductors laid in place between the walls and squeezed by the screw.
It is of considerable practical importance to maintain assembly of the parts of a lay-in connector when it is not in use. One common way of doing this is to use a screw whose diameter is greater than the separation between the walls of the base member, that separation being locally enlarged so as to form recesses in the opposite wall surfaces to receive the screw. So long as the screw is received in those recesses, the screw-bearing member cannot slide out of place. It then becomes necessary to unscrew the screw for retracting it from such recesses before the screw-bearing member can be removed in preparation for laying-in a conductor. The screw diameter must be larger than the average space between the walls of the first member. As a result, the design of that form of lay-in connector has a number of constraints in connection with the feature of preventing its disassembly, where those constraints are unrelated to -- and may encroach upon -- the considerations involved in the design of the connector for its prime function, i.e., making a connection.